It's a closure. The lisp equivalent is also a closure, and the JS equivalent is a function (which is a closure as they can refer to variables in the scope they'

It's a closure. The lisp equivalent is also a closure, and the JS equivalent is a function (which is a closure as they can refer to variables in the scope they're defined in. To test this define a function inside a function and reference variables defined in the outer function, and return the inner function).